Drag coefficient

About: Drag coefficient is a research topic. Over the lifetime, 14471 publications have been published within this topic receiving 303196 citations. The topic is also known as: drag factor.

Calculation of Vortex Shedding Past a Square Cylinder with Various Turbulence Models

Abstract: The vortex-shedding flow past a square cylinder at Re = 22.000 was calculated with various turbulence models. The 2D periodic shedding motion was resolved in an unsteady calculation, and the superimposed stochastic turbulent fluctuations were simulated both with the k — e eddy-viscocity model and with a Reynolds-stress equation model. For both models, the viscosity-affected near-wall region was either bridged by wall functions or was resolved with a simpler one-equation model using a prescribed length-scale distribution. The k — e model with wall functions does not yield unsteady vortex motion while the other model variants do. The two-layer k —e model underpredicts severely the periodic fluctuations and also the Strouhal number and drag coefficient. The Reynoldsstress-equation models yield considerably better agreement with experiments, but tend to overpredict the periodic fluctuating motion and also miss some other details of the flow behaviour.

The flow of viscoelastic fluids past a cylinder : finite-volume high-resolution methods

Abstract: Accurate solutions are obtained with the numerical method of Oliveira et al. [J. Non-Newtonian Fluid Mech. 79 (1998) 1] for the inertialess plane flow around a confined cylinder. This numerical procedure is based on the finite-volume method in non-orthogonal block-structured meshes with a collocated arrangement of the dependent variables, and makes use of a special interpolation practice to avoid stress‐velocity decoupling. Two high-resolution schemes (MINMOD and SMART) are implemented to represent the convective terms in the constitutive equations for the upper convected Maxwell and Oldroyd-B fluids, and the resulting predictions of the drag coefficient on the cylinder are shown to be as accurate as existing finite-element method predictions based on the supposedly very accurate h-p refinement technique. Numerical uncertainties are quantified with help of Richardson’s extrapolation technique and the orders of convergence of the differencing schemes are established and shown to be second-order accurate. Calculations performed with a wake-refined mesh predicted the variation of the maximum longitudinal normal stress in the wake as De 3 and De 5 depending on Deborah number. © 2001 Elsevier Science B.V. All rights reserved.

Anomalous hydrodynamic drafting of interacting flapping flags.

Abstract: In aggregates of objects moving through a fluid, bodies downstream of a leader generally experience reduced drag force. This conventional drafting holds for objects of fixed shape, but interactions of deformable bodies in a flow are poorly understood, as in schools of fish. In our experiments on "schooling" flapping flags, we find that it is the leader of a group who enjoys a significant drag reduction (of up to 50%), while the downstream flag suffers a drag increase. This counterintuitive inverted drag relationship is rationalized by dissecting the mutual influence of shape and flow in determining drag. Inverted drafting has never been observed with rigid bodies, apparently due to the inability to deform in response to the altered flow field of neighbors.

The turbulent structure of the bottom boundary layer in a tidal current

Abstract: Summary. Measurements of turbulence in the neutrally stratified bottom boundary layer of a tidal current are described. It is shown that whereas the bottom boundary layer is similar to its atmospheric counterpart, in terms of appropriately scaled spectra of the turbulent velocity fluctuations and the Reynolds stress, there is less evidence to suggest that it is structurally similar when measured in terms of the Reynolds stress tensor components. These differences appear to be more pronounced in deep flows where there is some evidence to suggest that the indices of structural similarity may vary over the tidal cycle; this behaviour may be due in part to the presence of inactive motions in the boundary layer. The statistical properties of the turbulence are described and in particular the high sampling variability of the Reynolds stress is shown to be associated with intermittently large momentum fluxes occurring in the boundary layer. The use of an intermittency factor in determining the burst period is also discussed. Suspended sediment is shown to have no effect on the turbulent structure of this example of a boundary layer. Estimates of the drag coefficient for a range of sediment types and bed forms have been obtained and finally it is shown that levelling errors are a major source of inaccuracy in boundary layer stress measurements.